(578g) Simulated Temperature Programmed Desorption of Acetaldehyde on CeO2(111): Evidence for the Role of Oxygen Vacancy and Hydrogen Transfer

Typical biomass processing routes produce mixtures containing large fractions of small organic oxygenates including aldehydes, carboxylic acids, ketones and alcohols. However, their low molecular weights and high oxygen contents are undesirable in the production of fuels and higher value chemicals. Recently reducible oxides have been suggested as potential catalysts for the conversion of these organic oxygenates, via selective C-C coupling and deoxygenation reactions. We have studied the temperature programmed desorption (TPD) of acetaldehyde adsorbed on partially reduced CeO₂(111) in detail using micokinetic modeling based on self-consistent, periodic density functional theory calculations at the GGA+U-PW91 level. The outcomes of our microkinetic model are in close agreement with the observed desorption activities in TPD and infrared evidence for surface species. According to our proposed mechanism, oxygen vacancies play the critical role of activating the carbonyl bond by stabilizing the negatively charged O atom with exposed Ce⁴⁺, which facilitates the transfer of hydrogen atoms among the organic moieties and the formation of enolate that enables C-C coupling reactions under appropriate conditions.